A variety of liquid or fluid level indicators are known for monitoring and displaying the level of a liquid or fluid in a container in applications where the fluid is not directly visible. One such device is a visual fluid indicator which comprises a flat glass fluid level gauge which provides an indication of the vertical level of fluid in a container. Typically, the flat glass fluid level gauge is mounted vertically alongside the container and is connected at both its top and bottom ends with the interior of the container. The level of fluid in the container, when occupying levels between the top and bottom of the fluid level gauge, may be viewed through the glass in the gauge.
Another type of fluid level indicator is a magnetic fluid indicator which employs a plurality of magnetically responsive indicator elements which move in response to movement of a magnetic float contained within a fluid container (see, e.g. U.S. Pat. Nos. 3,964,312 and 4,483,193). The magnet is typically disposed in a vessel, such as a pipe, which is vertically mounted to the outside of the container and which is connected to the interior of the container at its top and bottom ends. The vertical position of the floating magnet changes as the level of fluid in the container, and thus the pipe, changes. The magnetically responsive indicator elements positioned at the level of the magnet are actuated in response to this movement. The indicator elements are typically painted or coated on the side which is visible when actuated to provide a visual indication of the fluid level.
Illuminators for enhancing the visibility of such fluid level indicator devices are known, typically including an incandescent bulb for applying light to the device. For example, in the visual fluid indicator described above, illuminators are known which comprise an illumination source and a reflector which reflects light provided by the illumination source onto the back of the fluid level gauge. For example, Series GA illuminators manufactured by Jerguson.RTM., which are designed to improve the readability of flat glass fluid level gauges in poorly lighted areas, include an incandescent light bulb and a large wedge-shaped reflector mounted behind the fluid level gauge. The output of the light source is spread by the wedge-shaped reflector and applied to the back of the gauge.
The above-described illuminator, however, suffers from several drawbacks. Installation typically requires the illuminator to be bolted to the gauge, and the bolts tightened to a specific torque value. If the illuminator is attached to the gauge using the same bolts that hold the gauge together, the torque applied to the gauge may be affected by the illuminator. Installation is also made difficult due to the size and weight of the incandescent bulb and the large wedge-shaped reflector.
In addition, the wedge-shaped reflector of the known illuminator does not evenly distribute light from the light source across the length of the wedge. This phenomenon is particularly noticeable if a string of wedge-shaped illuminators are connected end-to-end in a particular application to illuminate a longer gauge. In any particular reflector of the string, the brightest point of the illumination occurs at the point opposite the light source and the dimmest point occurs at the points furthest away from the light source. The human eye adjusts to these bright spots which greatly affects readability in the dimmer regions. Moreover, the wedge-shaped reflector tends to catch the wind in external environments which may apply unacceptable levels of stress to the vertical gauge to which it is attached. Still further, the bulky size of the wedge-shaped reflector poses a risk of being inadvertently dislodged from its mounting by service personnel.
In addition, the use of an incandescent bulbs in known illuminators requires recurrent maintenance. Because the fluid level gauges are used in environments where processing equipment such as pumps are operating, vibration may cause filament damage and eventual bulb failure. Vibration other than that caused by the processes being monitored, such as that caused by wind as described above, can also lead to bulb failure. Even absent such vibration, the incandescent bulbs are typically rated for only about a 2500 hour lifetime, in part because they operate at relatively high voltages. The environments in which these illuminators are installed are typically operated around the clock, and thus the bulbs must be replaced every 100 days or so. Because the illuminators are often installed in areas which are not easily accessed, recurrent maintenance of the illuminators is a problem.
Moreover, because level indicator illuminators are often used in wet environments where combustible gases are present, the potential for explosion must also be accommodated by the illuminator design. Wet environments increase the risk of illuminator failure. If the illuminator has become heated as a result of continuous operation, and the outer enclosure of the illuminator begins to get wet, the enclosure begins to cool, causing air contained therein to cool and contract. The resulting vacuum draws moisture which accumulates on the outer enclosure into the interior cavity of the enclosure. If any of this moisture comes into contact with the hot illumination source, the illumination source is likely to explode. Although an explosion-proof enclosure will likely contain the explosion, the exploding bulbs present a maintenance problem in that they must repeatedly be replaced, especially in wet illuminator environments.
It is therefore also desirable that illuminators for fluid level indicator devices be waterproof and explosion-proof. Standards, such as those established by the National Electrical Manufacturers Association (NEMA), have been promulgated by which devices such as illuminators may be rated in terms of being waterproof and explosion-proof.
Accordingly, it is an objective of the present invention to provide a waterproof and explosion-proof illuminator for a fluid level gauge which provides even illumination across the entire fluid level gauge, requires little maintenance, is lightweight and of manageable size to facilitate easy attachment and detachment from a fluid level gauge, and is suitable for both interior and exterior applications.